Electrode assembly



2 Sheets-Sheet March 10, 1942. c. c. HERsKlND ELECTRODE ASSEMBLY FiledJuly 2, 1940 Inventor: Carfl C.Her's| incl, by .WWA/6. AWM

His Attorney'.

March 10, 1942.

C.\C. HERSKIND ELECTRODE ASSEMBLY Filed July 2, 1940 2 Sheets-Sheet 2Inventor. Carl C. HersKihd', v b9 .7V His ttorneg.

ge; JwMW//f/ V l v I1 w n A R Patented Mar. 10, 1942 UNITED STATES POFFICE 2,275,852 V ELECTRODE ASSEMBLY Carl C. Herskind, Schenectady, N.Y., assignor to General Electric Company, a corporation of New YorkApplication July 2, 1940, Serial No. 343,532

(Cl. Z50-27.5)

6 Claims.

initiating the main discharge at controlled intervals.

In devices of the character above specied it frequently proves desirableto employ, in addition to the main discharge electrodes and theimmersion ignitor electrode, an auxiliary anode which serves lto augmentthe basic discharge controlling means. One typical use of such anauxiliary anode is to lessen the current loading of the ignitorelectrode in the period following the performance of the lattersdischarge-initiating function. Another use is as a terminal for acyclically renewed holding-arc which serves to assure the maintenancelof the principal discharge under circumstances tending to cause theundesired extinguishment of the latter.

It is a particular object of the present invention to provide animproved electrode assembly in which an immersion-ignitor electrode andan auxiliary anode are combined in a unitarily mounted arrangement whichnot only possesses the manufacturing advantages of compactness andsimplicity but which also assures that both electrodes shall functioneectively in their intended manner.

An important feature of the invention consists in an arrangement wherebythe ignitor electrode and the auxiliary anode are supported by a commonmounting means.

A further important feature, ancillary to the above, includes the use aspart of the electrode mounting means of a hollow tubular housing whichextends outwardly from a lateral wall of the discharge envelope andwithin which the auxiliary anode is positioned. As will be more fullyexplained hereinafter, this construction is beneficial not only from amechanical standpoint but also in respect to the protection against ionbombardment which it affords to the auxiliary anode.

The aspects of the invention which I consider to be novel are pointedout with particularity in the appended claims. The invention itself,together with further objects and advantages thereof, may best beunderstood by reference to the following description taken in connectionwith I the accompanying drawings, in which Fig. l is a view in partialsection of a discharge device suitably embodying the invention; Fig. 2is an enlarged sectional View of a portion of the structure representedin Fig. 1; Fig. 3 and 4 are respectively v cross-sectional views takenon lines 3-3 and 4 4 of Fig. 2; and Fig. 5 is a diagrammatic circuitrepresentation illustrating a typical mode of use of the invention.

Referring particularly to Fig. 1, there is shown a discharge devicehaving as an envelope an elongated metal cylinder II) which is closed attop and bottom by appropriate transverse wall portions, the lower wallportion being illustrated at II. Within the envelope and at the lowerend thereof there is provided a cathode I2 in the form of a pool ofmercury which is in direct contact with the floor of the envelope. Thiscooperates with an anode which is shown in part at I3, and which may besuitably constituted of graphite. A graphite baiiie or shield l5, alsousable under some circumstances as a control grid, surrounds the anodeI`3 and serves in the use of the device to protect the anode fromexcessive ion bombardment. The anode I3 and the bafe I5 are respectivelyconnected with externally accessible current supply conductors of whichthe externally visible parts are indicated at IS and I1.

A further baITle I8 of imperforate character is supported over thecentral portion of the cathode and acts to prevent mercury sprayed fromthe cathode from being projected on the anode where it might lead toinverse breakdown of the device. Mercury which condenses on and flowsdown the walls of the envelope I0 is enabled to return to the central oractive portion of the cathode by passing under the lower edges of a pairof metal rings I9. These rings provide a trap for solid impurities,which, after being Washed down the envelope walls, float to the mercurysurface and are caught in the areas outside the rings.

In operation, the discharge chamber is maintained at a fixed operatingtemperature by means of a cooling coil 20 provided in direct contactwith the walls of the discharge envelope, a suitable cooling fluid suchas tap water being circulated through the coil to carry away the excessheat generated by the discharge. In order to prevent condensation ofmoisture on the surfaces of .the cooling coil 20, the coil is coveredwith` an, external casing which includes an outer metal sheath 22 and alayer of thermally insullating material 23, for example, asbestos paper,

which is interposed between the inner surface of the sheath 22 and thecoil 20. A number of brackets, indicated at 25, are provided for thepurpose of supporting the coil 20 in proper relation to the dischargeenvelope. A floor plate 2l which is secured to the lower extremity ofthe metal cylinder Ill serves to complete the enclosure of the dischargeenvelope and to protect it from accumulation of dirt and moisture. Thisplate also provides a mounting surface for the apparatus as a whole andforms an externally accessible point at which current supply conductors(not shown) for the cathode I2 may be ccnnected.

In addition to the elements so far described, the apparatus of Fig. 1includes as a sub-assembly thereof, the combination of an immersionignitor and an auxiliary anode 3|. The ignitor electrode 30 is incontact with the surface of the mercury and consists of a materialhaving a high specific resistivity in comparison with mercury. It maysuitably comprise silicon carbide or boron carbide or a combination ofthese substances with other materials. It is a known property of anelectrode of this character that when impressed with a positivepotential, it acts to establish a cathode spot on the mercury surfaceand thus facilitates the initiation of the principal discharge. Theauxiliary anode 3| suitably consists of an annular body of graphite andis adapted to cooperate with the ignitor electrode 30 either inrelieving the same of excessive current loading during the periodimmediately following initiation of a discharge or, in some cases,offacilitating the maintenance of the discharge once it is initiated.

The mounting structure which supports the electrodes 30 and 3| includesa tubular metal housing 33 which extends outwardly from the lateral wallof the discharge envelope and which is integrally joined to the envelopeas by being peripherally Welded thereto. Extending axially through thetubular housing 33 there is provided a rigid current supply conductor 40(see Fig. 2) which connects at its inner extremity with the ignitorelectrode 3|) so as to support the latter in contact with the cathodeI2. The auxiliary anode 3| surrounds this conductor and is supported ininsulatingly spaced relation thereto by a second conductor in the formof a metal tube 42 which also extends outwardly through the end of thehousing 33. As appears most clearly in Figs. 2 and 3, the anode isscrew-threaded on one end of the conductor 42 and is maintained in fixedrelation thereon by means of a suitable key 44.

The outer extremity of the housing 33 is sealed by a closure member inthe form of an annular metal diaphragm 34 which supports the auxiliaryanode 3| and the ignitor-electrode 36 in a manner shortly to bedescribed. This diaphragm is peripherally clamped between an annularplate 36 and a flange 31 which extends outwardly from the housing 33 atits outer extremity. The parts 36 and 31 are forced into engagement withthe diaphragm 34 by means of bolts 38 or by other suitable joiningmeans. If desired, a deformable gasket arrangement (not shown) may beemployed to improve the seal existing between the surface of thediaphragm 34 and the opposing surface of the flange part 31.

The diaphragm 34 is provided at its inner periphery with a flange or lipwhich engages and is hermetically joined to a cylindrical metal part 46extending outwardly from the extremity of the housing 33. Anothercylindrical metal part having a rst portion 48 which is of the samediameter as the part 40 and a second portion 43 of reduced diameter ispositioned in partially telescoped relationwith respect to the part 46.A quantity of vitreous insulating material 50, preferably of thecomposition known as Micalex (i. e., a mixture of mica and lead borate).is interposed between the parts 46 and 49 to establish a hermetic sealbetween them and to maintain them in rigid assembly. Through a screwthreaded connection with this assembly the conductor 42 and theauxiliary anode 3| are supported from the diaphragm 34. The conductor 4Dis also supported indirectly from the diaphragm by being connected to ametal plug 52 which interflts with and is rigidly sealed into the part48, the seal consisting of a body of Micalex 53.

In forming the electrode-mounting structure described in the precedingparagraph the metal part 46, after being heated to a high temperature,is placed in a cylindrical mold, and a measured quantity of fusedMicalex is then poured into the mold. 'I'his is followed by the part48-49, also at high temperature. A second measured quantity of fusedMicalex is then placed in the mold, and the part 53 is finallyintroduced. The contents of the mold are then subjected to pressure inorder to force them into sealing engagement. After cooling, the sealassembly is removed from the mold and machined to the form shown in Fig.2. If desired in order to assure the better adherence of the metal partsto the Micalex, their surfaces may be preliminarily serrated as shown.The metal parts are preferably constituted of an iron alloy containingabout 25% chromium so as to provide at least an approximate match to theexpansion characteristics of the Micalex.

By virtue of the fact that the auxiliary anode 3| is within the confinesof the tubular housing 33 it is at least partially shielded from thepossibility oi bombardment due to ionization within the dischargeenvelope. In the use of the anode either as a relieving electrode forprotecting the ignitor element 30 from the effects of excessive currentconduction or as a terminal for a cyclically renewed holding arcassisting the maintenance of the main discharge this is an importantfactor in view of the necessity of permitting the anode 3| to attain anegative potential at some part of the discharge cycle. Excessive ionbombardment at such a time has a tendency to establish a cathode spot onthe surface of the anode, thus rendering it electron-emissive andoccasionally leading to an inverse discharge of harmful character. Withthe preferred structureillustrated this possibility is additionallyguarded against by the provision of a current permeable baffle in theform of a perforated graphite disk 55 which is supported on theconductor 40 at a point between the surface of the auxiliary anode 3|and the interior of the discharge envelope. By this arrangement, ionsproceeding toward the auxiliary anode are in large measure interceptedby the intervening surfaces of the baffle.

Exposure of the conductor 40 to the discharge space is found to lead todisintegration of the conductor material, and it is consequentlyadvantageous to enclose the conductor within a metal shield 51. Thisshield is supported in spaced relation to the conductor by means ofinsulating washers 58 and 59 which are suitably constituted of lava. Thewashers are maintained in position by the cooperative action of studs orbarbs 60 punched out of the surfaces of the shield 51 and a pair ofmetal sleeves 6| and 62 which are welded or otherwise secured to theconductor 40. A flange G3 which is secured to the end of the shield 51nearest the baiile 55 serves additionally to lessen the exposure of theauxiliary anode 3| to the main discharge space.

In addition to the advantages which the invention possesses from anelectrical standpoint, it has the important mechanical advantage ofproviding a single mounting and lead-in structure for both theignitor-electrode and the auxiliary anode. With the arrangementdescribed, only a single port need be provided in the wall of thedischarge envelope, this being a feature which has important advantagesfrom the standpoint of manufacturing simplicity and economy.

If desired, the construction above described may be readily adapted topermit adjustmentof the position of the ignitor-electrode by meanswholly external of the discharge envelope. Such means may comprise, forexample, a pair of oppositely directed thrust screws 64 and 65 (Fig. I)which are appropriately supported from the annular plate 36 and whichact to cause tilting action of the electrode-supporting structure aboutthe diaphragm 34 as a fulcrum. The diaphragm may readily be madesuiciently ilexible to permit enough motion to occur to enable thedegree of immersion of the ignitor 30 to be adjusted to the point whichgives best operation.

The mode of use of the invention may best be understood by reference toFig. 5 which illustrates the application of the invention in a circuitof a type which is fully described and claimed in application S. N326,924, filed March 30, 1940, in the name of C. C. Herskind. It is thefunction of the circuit to convert alternating current derived from asource into direct or pulsating unidirectional current at terminals 1|.For the purpose of accomplishing this conversion there is provided adischarge device 13 which, although shown diagrammatically, isasportion'of the operating cycle and its lifefwill be consequentlyprolonged. l

Upon the reversal of the potential supplied by the main source 10 thetube 13 will be rendered non-conducting, and the entire cycle will berepeated at recurrent intervals.

A further use for the invention is in a circuit which utilizes theauxiliary anode as a terminal for aicyclically renewed holding-arcrather than as a means for relieving the ignitor electrode, such acircuit being described, for example, in application S. N, 343,966 ledJuly 5, 1940, as a joint application of M. Edwards and O. W. Livingston.In both the uses above referred to, the auxiliary anode necessarilyattains a negative potential 'at some part of the operating cycle and issusceptible to bombardment by positive ions originating in the dischargespace. The structural arrangement specified herein assures theprotection of the auxiliary anode from direct exposure to such ions andthus minimizes the danger of arc-back arising from this cause.

While the invention has been described by reference to a particularembodiment thereof, it will be understood that numerous modificationstherein may be made by those skilled in the art without actuallydeparting from the invention. I, therefore, aim in the appended claimsto cover all such equivalent variations as come within the true spiritand scope of the foregoing disclosure.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is:

1. In a discharge device which comprises a main anode, a mercury poolcathode and an envelope enclosing said anode and cathode, the

i combination which includes an immersion-ignitor sumed to be of thestructural character of the device illustrated in Fig. 1. It includes ananode 14, a cathode 16, an immersion ignitor 11 and an auxiliary anode18 which is supported in a laterally extending housing 19 andwhich isshielded by baile 80.

The anode 14 is connected to one terminal of a transformer 15 excitedfrom the source 10, and the cathode 16 is connected directly to thepositive terminal of the direct current part of the system.

For initiating a discharge through the device 13 at cyclically recurrentintervals there is provided as a source of control impulses a so-calledpeaking transformer 8|. One terminal of the secondary of thistransformer is connected to the cathode 16 and the other terminal isconnected to the immersion ignitor electrode 19. The connection to theignitor is made through a thermionic rectier 82 which permits onlyunidirectional current flow to the ignitor electrode, and a resistance83 connected in series with the electrode 19 serves to limit the currentow thereto.

Assuming that the electrodes 14 and 11 attain positive potentials atconcurrent instants, a cathode spot will be initiated by the electrode11, and conduction through the tube will take place. However, as soon asan appreciable amount of ionization is established in the dischargespace, an auxiliary discharge to the anode 18 will occur, and, becauseof the low impedance of the circuit connecting with this anode ascompared with the circuit by which the ignitor is supplied, the currentto the ignitor will immediately fall to a low value. In this Way theignitor will be relieved of current fiow during the major electrode incontact with the mercury cathode, a hollow housing projecting outwardlyfrom a lateral wall of the envelope and hermetically'joined thereto, arigid current supply conductor extending from said ignitor electrodeoutwardly through said housing and serving to support said ignitor, anauxiliary anode comprising a body of conductive material which surroundsthe said conductor at a point within the connes of said housing, wherebysaid auxiliary anode is at least partially shielded from the possibilityof bombardment due to ionization within the envelope, said auxiliaryanode being insulatingly spaced from said conductor, and a secondconductor extending within said housing for supplying current to theauxiliary anode.

2. In a discharge device which comprises a main anode, a mercury poolcathode and an envelope enclosing said anode and cathode, thecombination which includes an immersion ignitor electrode in contactwith the mercury cathode, a tubular housing extending outwardly from alateral wall of said envelope, a rigid current supply conductorextending from said ignitor electrode outwardly through said tubularhousing and serving to support the ignitor electrode, an auxiliary anodecomprising a body of conductive material which surrounds said conductorat a point Within the confines of said housing, a tubular conductorcoaxial with said rst named conductor and extending outwardly from saidauxiliary anode through the end of said tubular housing for supplyingcurrent to the auxiliary anode, a closure member for sealing theextremity of said housing and means mechanically supporting saidignitor-electrode and said auxiliary anode from said closure memberthrough the said current supply conductors.

3. In a discharge device which comprises a main anode, a mercury poolcathode and an envelope enclosing said anode and cathode, thecombination which includes an immersion-ignitor electrode in contactwith the mercury cathode, a tubular housing extending outwardly from alateral wall of the envelope, a rigid current supply conductor extendingfrom said ignitor electrode outwardly through said housing and servingto support the ignitor electrode, an auxiliary electrode comprising abody of conductive material which surrounds the said conductor at apoint within the connes of said housing, whereby the auxiliary anode isat least partially shielded from the possibility of bombardment due toionization within the envelope, said auxiliary anode being insulatedfrom the said lead-in conductor, means for supplying current to saidauxiliary anode, and a current permeable bailie also within the connesof the housing and interposed between the auxiliary anode and theinterior of the envelope for additionally shielding the anode.

4. In a discharge device which comprises a main anode, a mercury poolcathode and an envelope enclosing said anode and cathode, thecombination which includes an immersion-ignitor electrode in contactwith the mercury cathode, a hollow housing projecting outwardly from thelateral wall of the envelope and hermetically joined thereto, aconductor extending from said ignitor electrode outwardly through saidhousing and serving to supply current to the electrode, an auxiliaryanode comprising a body of conductive material which surrounds the saidconductor at a point within the connes of said housing, whereby saidauxiliary anode is at least partially shielded from the possibility ofbombardment due to ionization within the envelope, said auxiliary anodebeing insulatingly spaced from said conductor, and a second conductorextending within the said housing for supplying current to the auxiliaryanode.

5. In a discharge device which comprises a main anode, a mercury poolcathode and an en- `velope enclosing said anode and cathode, thecombination which includes an immersion ignitor electrode in contactwith the mercury cathode, a tubular housing extending outwardly from alateral wall of said envelope, a rigid current supply conductorextending from said ignitor electrode outwardly through said tubularhousing and serving to support the ignitor electrode, an auxiliary anodecomprising a body of conductive material which surrounds said conductorat a point within the confines of said housing, a second conductorextending from said auxiliary anode outwardly through the end of saidtubular housing for supplying current to the auxiliary anode, a closuremember for sealing the extremity of said housing and means mechanicallysupporting said ignitor and said auxiliary anode from said closuremember through the said current supply conductors.

6. In a discharge device which comprises a main anode, a mercury poolcathode and an envelope enclosing said anode and cathode, thecombination which includes an immersion ignitor electrode in contactwith the mercury anode, a tubular housing extending outwardly from awall of said envelope, a rigid current supply conductor extending fromsaid ignitor electrode outwardly through said tubular housing andserving to support the ignitor electrode, an auxiliary anode comprisinga body of conductive material which surrounds said conductor at a pointwithin the confines of said housing, a second conductor extending fromsaid auxiliary anode outwardly through the end of said tubular housingfor supplying current to the auxiliary anode, a deformable closuremember for sealing the extremity of said housing, means mechanicallysupporting said ignitor electrode and said auxiliary anode from saidclosure member through the said current supply conductors and means forcontrollably deforming said closure member to adjust the degree ofcontact of the ignitor electrode with the mercury cathode.

- CARL C. HERSKIND.

